The invention relates to Superpave Asphalt Mix design.
The design of asphalt paving mixes mainly involves selecting and proportioning materials to obtain the desired properties in the finished construction. The overall objective for the design of asphalt paving mixes is to determine an economical blend of binder and gradation of aggregates, within the limits of the project specifications, and an asphalt paving mixture that yields a mix having: sufficient asphalt to ensure a durable pavement; sufficient mix stability to satisfy the demands of traffic without distortion or displacement; sufficient voids in the total compacted mix to allow for a slight amount of additional compaction under traffic loading without flushing, bleeding, and loss of stability, yet low enough to minimize the intrusion of harmful air and moisture; and sufficient workability to permit efficient placement of the mix without segregation.
From October 1987 through March 1993, a DOT program known as Strategic Highway Research Program (SHRP) conducted research effort to develop new ways to specify, test, and design asphalt materials. The final product of the SHRP asphalt research program is a system referred to as Superpave, which stands for Superior Performing Asphalt Pavements. It represents an improved system for specifying the components of asphalt concrete, asphalt mixture design and analysis, and asphalt pavement performance prediction.
Superpave mix design is a structured approach consisting of the following four steps:
selection of materials,
selection of design aggregate structure,
selection of design asphalt binder content, and
evaluation of moisture susceptibility.
The selection of materials is accomplished by first selecting a Performance Grade asphalt binder for the project climate and traffic conditions. Superpave binders are designated with a high and low temperature grade, such as PG 64-22. For this binder, xe2x80x9c64xe2x80x9d is the high temperature grade and is the 7-day maximum pavement design temperature in degrees centigrade for the project. The low temperature grade, xe2x80x9cxe2x88x9222,xe2x80x9d is the minimum pavement design temperature in degrees centigrade. Both high and low temperature grades are established in 6-degree increments. Thus, the binder grade is an indication of the project-specific temperature extremes for which the asphalt mixture is being designed.
In addition to climate, traffic speed and traffic level may also influence Superpave binder selection. A project with slow moving or stationary traffic would require a binder with one or two higher temperature grades than would otherwise be selected on the basis of climate alone. Projects with very high traffic levels in excess of 30 million 80 kN equivalent single axle loads would also require an increase in high temperature binder grade.
In one aspect, a method for automating mix design includes estimating volumetric properties for one or more mix designs; running one or more tests on the mix design using a gyratory compactor; digitally collecting data for each gyration from the gyratory compactor; and selecting an optimum mix based on the gyration data.
In a second aspect, a method for asphalt mix design includes predicting properties associated with a mix of volumetric properties; verifying properties of the mix by digitally collecting data for each gyration from a gyratory compactor; and selecting an optimum mix based on the gyration data.
In another aspect, a mix design system includes a gyratory compactor; and a computer coupled to the gyratory compactor, the computer having computer readable code to estimate volumetric properties for one or more mix designs; run one or more tests on the mix design using the gyratory compactor; digitally collect data for each gyration from the gyratory compactor; and select an optimum mix based on the gyration data.
Implementations of the above systems and methods may include one or more of the following. The above system can be used to design a Superpave mix. Five asphalt mixture types are specified in Superpave according to nominal maximum aggregate size: 9.5 mm, 12.5 mm, 19 mm, 25 mm, and 37.5 mm. Once binder and aggregate materials have been selected, various combinations of these materials are evaluated using a gyratory compactor. Three, and sometimes more, trial blends are evaluated. For example, assume that four aggregate stockpiles have been selected for use.
Once the trial blends have been established, a trial asphalt binder content is selected for each blend. The trial asphalt binder content is selected using an estimation procedure contained in Superpave or using a method for predicting volumetric properties disclosed in U.S. Pat. No. 5,943,234, the content of which is hereby incorporated by reference.
Next, two specimens of each trial blend are batched and compacted in the gyratory compactor and data is automatically collected, as detailed below. In addition, two specimens of each trial blend are produced and used to measure maximum theoretical specific gravity. The volumetric and densification characteristics of the trial blends are analyzed and compared with Superpave mix design criteria. The best trial blend that meets these criteria can be selected as the design aggregate structure.
The next step involves selection of the design binder content four different asphalt contents are tested(ACxe2x88x9205)(AC)(AC+0.5)(AC+1) after calculating volumetric properties, Optimum Binder is Calculated at 4% Air Void. The design aggregate structure containing the designed-selected blend at optimum asphalt binder content becomes the design asphalt mixture.
Advantages of the system may include one or more of the following. The system improves the efficiency of the user by minimizing the use of laboratory trial and error procedures.